Tim wrote in asking if he should use roofing paper on his roof in addition to Ice and Water shield.
Well Tim, there are not a lot of hard and fast rules in roofing but there are some guidelines and some little things that definitely make a better more problem free roof.
First, on the front edge of the roof overhang you should nail on a Drip Edge. This metal flashing runs a couple of inches up the roof, out over the edge and then bends down and back. Water coming off the edge will be directed off the roof (into the rain gutter) and not allowed to sneak back under the shingles. Too often this important detail is forgotten.
Second, if you have any icing problems or are worried that you might have, put on a rubber membrane that is stuck to the roof with a self adhesive side to the rubber. This is what is called the Ice and Water shield. It is not absolutely necessary but it is extra protection over that area of the roof that could potentially have water backing up from roof edge ice dams, up and under the shingles. When nails are driven through, it seals around the nails. How far up the roof should it go? Many people say the first three feet, but that is only because it comes in three feet wide roles. Some people put it over the entire roof but that is expensive, and if you don't have ideal attic ventilation, this could cause the deck to rot under the rubber.
How far up the roof you should put Ice and Water shield is actually dependent on the slope and the overhang of the roof. Look at the photos above to see how to figure out if three feet is enough or if you might need to apply a bit more. On the side of the house, measure horizontally back from the outside wall 18 inches. Then run a line straight up to the roof. The point on the roof where this line lands is the top end of the Ice and Water shield. So you can see why I say that the distance from the bottom edge of the roof is dependent on the slope and overhang of the house. If three feet is anywhere near this mark, use three feet. If you are missing a foot, cut off smaller strips and overlap them with the first one.
One more detail. The ice and water shield should stick firmly over the top of the drip edge on the soffit edge of the roof.
Third, roofing paper is a good idea over the rest of the roof, but rarely required. It is not expensive but it does give an extra line of defence against water intrusion and it gives a slip layer between the roof deck and the shingles that will help to prevent wear from expansion and contraction. I would always put it on a roof, even when it is not required. If you are not using the Ice and Water shield, I would put roofing paper over the entire roof.
Fourth, you need to put a drip edge on the remaining sloped sides of the roof, over the building paper and over the ice and water shield. Then you put on the shingles. Those are the ingredients for a quality roofing job -- together with good flashings of course.